On Fri, Jul 25, 2014 at 01:16:39PM -0700, Jesse Barnes wrote: > > To allow managing external TLBs the MMU-notifiers need to > > catch the moment when pages are unmapped but not yet freed. > > This new notifier catches that moment and notifies the > > interested subsytem when pages that were unmapped are about > > to be freed. The new notifier will only be called between > > invalidate_range_start()/end(). > > So if we were actually sharing page tables, we should be able to make > start/end no-ops and just use this new callback, assuming we didn't > need to do any other serialization or debug stuff, right? Well, not completly. What you need with this patch-set is a invalidate_range and an invalidate_end call-back. There are call sites of the start/end functions where the TLB flush happens after the _end notifier (or at least can wait until _end is called). I did not add invalidate_range calls to these places (yet). But you can easily discard invalidate_range_start, any flush done in there is useless with shared page-tables. I though about removing the need for invalidate_range_end too when writing the patches, and possible solutions are 1) Add mmu_notifier_invalidate_range() to all places where start/end is called too. This might add some unnecessary overhead. 2) Call the invalidate_range() call-back from the mmu_notifier_invalidate_range_end too. 3) Just let the user register the same function for invalidate_range and invalidate_range_end I though that option 1) adds overhead that is not needed (but it might not be too bad, the overhead is an additional iteration over the mmu_notifer list when there are no call-backs registered). Option 2) might also be overhead if a user registers different functions for invalidate_range() and invalidate_range_end(). In the end I came to the conclusion that option 3) is the best one from an overhead POV. But probably targeting better usability with one of the other options is a better choice? I am open for thoughts and suggestions on that. Joerg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>